Hydraulic hoist control system



May 22, 1962 F. T. SMITH 3,035,414

HYDRAULIC HOIST CONTROL SYSTEM Filed Sept. 8, 1950 7 Sheets-Sheet 1COOLER RELIEF FUUR W/IY VALVE IN VEN TOR.

Fed 7757724272.

May 22, 1962 F. T. SMITH 3,035,414

HYDRAULIC HOIST CONTROL SYSTEM Filed Sept. 8, 1960 T Sheets-Sheet 2Neofra/ Gena /'on INVENTOR.

[Fed fflim/z, BY MQVMMVW May 22, 1962 F. T. SMITH HYDRAULIC HOISTCONTROL SYSTEM Filed Sept. 8, 1960 '7 Sheets-Sheet 3 3W ln ferme c/fa f21 /0 57 20/5/07 INVENTOR.

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HYDRAULIC HOIST CONTROL SYSTEM Filed Sept. 8, 1960 7 Sheets-Sheet 4 2)Ma x/mum Ala/sf Qcfis/hq g 115 A LCM/67? INVENTOR. [76d 2'' mzszf/z,

BY WM W w May 22, 1962 F. T. SMITH 3,035,414

HYDRAULIC HOIST CONTROL SYSTEM Filed Sept. 8, 1960 '7 Sheets-Sheet 5 1515 Ready For Hd/S/ am/grimy 0 a5 .34 Q a .1? V[ i 1% E s INVENTQR. F662.77 fimdh,

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HYDRAULIC HOIST CONTROL SYSTEM Filed Sept. 8, 1960 7 Sheets-Sheet 6 INVEN TOR. 176d .7 577ZLZ/z,

BY %MMJM-fl W F. T. SMITH HYDRAULIC HOIST CONTROL SYSTEM May 22, 1962 7Sheets-Sheet '7 Filed Sept. 8, 1960 ANM nited State This inventionrelates to improvements and innovations in hydraulic hoist systems foruse in controllably raising and lowering loads.

The present invention is a continuation-impart of my prior applicationSerial No. 796,527 filed March 2, 1959, now Patent No. 2,986,884 issuedJune 6, 1961. In that prior application I disclosed a hydraulic hoistcontrol system characterized by its excellent degree of controlobtainable through a wide range of speeds during both hoist raising andhoist lowering operations, and by the number of built-in safetyfeatures. Hoists built in accordance with my prior application haveproved extremely satisfactory in use especially where extraordinaryperformance and safety are requirements.

By means of the present invention there has been provided a simplifiedand less expensive hydraulic hoist control system which has goodcharacteristics with respect to ease of control, smoothness ofoperation, and safety so as to be entirely adequate for manyinstallations. By means of the present invention, it has been possibleto dispense with the sequence valve, counter-balance valve, and shuttlevalve which served important functions in the hydraulic control systemof my prior application. While the functions of these three componentsare no longer performed by corresponding units in the hoistcontrolsystem of the present invention, nevertheless, to a substantial degree aspecial four-way control valve compensates for these units which havebeen dispensed with.

Accordingly, the object of the present invention, generally stated, isthe provision of a relatively inexpensive hydraulic control system whichis capable of excellent control both in the raising and lowering andwhich has adequate safety features for all but a few specialinstallations.

More particularly, the object of the invention is the provision of sucha hydraulic hoist and control system which is built around a specialfour-way, open center, control valve which is the only special ornon-conventional component of the hoist system.

Certain other objects of the invention will, in part, be obvious, andwill in part appear hereinafter and become apparent in connection withthe following detailed der d scription thereof.

For a more complete understanding of the nature and scope of the presentinvention, reference may now be had to the following detaileddescription thereof taken in connection with the accompanying drawingswherein:

FIG. 1 is a diagram of a complete hydraulic hoist and control systemembodying the present invention;

FIG. 2 is a fragmentary view on an enlarged scale showing the conditionof the four way control valve of the system of FIG. '1 when it occupiesthe neutral position;

FIG. 3 is a view similar to FIG. 2 but showing the condition of thefour-way control valve when the hydraulic system is in condition forhoist raising but not at full capacity;

FIG. 4 is a view similar to FIG. 3 but showing the condition of thevalve in the maximum hoist raising condition;

FIG. 5 is a view similar to FIG. 2 but showing the con dition of thefour-way control valve in the condition when the brake is just ready tobe released to permit hoist lowering;

FIG. 6 is a view similar to FIG. 5 showing the condiate tion of thevalve during lowering at intermediate speed or load; and

FIG. 7 is a view similar to FIG. 6 showing the condition of the four-waycontrol valve for maximum rate of lowering.

Referring to FIG. 1 a positive displacement pump 5 of known type isshown which serves as a source of hydraulic pressure for operating thehoist. The pump 5 is driven by a uni-direction, constant speed motor 6such, for example, as a squirrel cage type electric motor. The driveshafts of the pump 5 and the motor 6 are suitably connected by acoupling indicated at 7.

Through a control system with suitable hydraulic circuitry to bedescribed below, the pump 5 delivers hydraulic fluid under pressure to apositive displacement hydraulic motor 10 of known type, such for exampleas an axial piston, rotary hydraulic motor. The motor 10 is reversiblein that it is driven in one direction during hoist raising and alsodriven in the reverse direction during hoist lowering. The outlet shaft11 of the motor 10 is suitably coupled to the input connection of a geartrain indicated diagrammatically at 12. The output connection of thegear train 12 is suitably connected to a cable drum of known typeindicated at 13. The mounting and interconnection of the gear train 12and the cable drum 13 may follow conventional hoist constructionpractice. The drum 13 is interconnected through the gear box with thecenter shaft 15 of a safety brake of known type indicated at 14, as isconventional.

The shaft 15 is mounted in the rotating element 16 of a free runningclutch, such as Sprague clutch which is free to rotate in one directiononly. In this case the brake shaft 15' is free to rotate in the hoistlifting direction.

The brake 14 has a brake drum 17 of relatively large diameter which maybe clamped in braking relationship from opposite sides by means of apair of brake shoes 18 mounted in the clamping arms 2ti-2t) hinged atthe bottom to a yoke 19.

The arms 20 are normally pulled together at the top continuously bymeans of a heavy compression spring 21 which is maintained undercompression between a disk 22 and a flat portion 23 on the adjacent arm20. The outer plate 22 is secured to the outer end of a rod 24, theinner end of which is provided with an eye whereby it is pivotallyconnected to the opposite arm 20. It will be seen that as the spring 21is retained under compression it continuously pulls the two arms 20together and thereby sets the brake shoes 18 on the drum 17.

It will be appreciated that the foregoing arrangement for keeping thebrake 14 ,se or on may be varied and means other than a compressionspring can be used although this is satisfactory and is highly reliable.A hydraulic cylinder unit 25 of known type may be utilized forovercoming the force of the spring 21 and separating the arms 20sufficiently to release the brake 14. Such a hydraulic cylinder unit 25is indicated as being interposed between the upper ends of the arms 20with a pressure line 26 extending thereto. It will be appreciated thatwhen fluid pressure of a predetermined value is admitted to the cylinder25 it will operate to overcome the force of the spring 21 and releasethe brake. If the pressure is admitted slowly the brake 14 can be verygradually released and an important operating advantage can be taken ofthis characteristic of the brake 14 as will be pointed out below.

Since under prolonged heavy duty operation the hydraulic fluid or oilwill undergo a considerable rise in temperature, it is desirable toprovide a cooler of known type such as that indicated diagrammaticallyat 27. Preferably all of the oil is returned to the tank or reservoirvia the cooler 27 through the return main or conduit 28. The dischargeside of the cooler 27 is connected by means of a conduit 30 with theinlet of an oil filter 31 disposed within the reservoir 8. By means ofthe cooler 27 and the filter 31 the hydraulic fluid is kept cool andclean.

The hydraulic control system or circuit for interconnecting the pump 5or other source of fluid pressure with the motor and brake 14 will nowbe described.

The principal component of the hydraulic control system is a four-waycontrol valve which is specially adapted for this particular invention.A first conduit comprised of sections 31 and 32 connect the center orintermediate pressure inlet port 33 of the valve 30 with the pressuredischarge connection of the pump 5. In one half of the valve 30 (thelower half as viewed in FIG. 1) there are a pair of valve ports, the oneadjacent the port 33 being indicated at 34 and the one that isnon-adjacent being indicated at 35. Similarly, in the other side of thevalve 30 (the upper half as viewed in FIG. 1) there are a second pair ofvalve ports, the one adjacent to the port 33 being indicated at 36 andthe one non-adjacent thereto being indicated at 37. The purpose andnature of each of the ports 3334353637 will be described below inconnection with FIGS. 17. All of the ports are of equal width and theyare separated from one another by lands of equal width.

The port 34 is connected to one of the two fluid connections of motor141 by means of a conduit 40. The particular connection to which conduit40 is connected is the one through which fluid exits during hoistraising and through which it enters during hoist lowering. Valve port 36is connected to the second fluid connection of the motor 10 through aconduit 41, the connection being that through which fluid enters duringhoist raising and through which it exits during hoist lowering. Portsand 37 are interconnected by a passageway 42 in the valve body whichcommunicates with the tank return line indicated at 28.

In addition to the conduits mentioned which communicate with the valveports 33-37 there is conduit 26 which communicates between conduit andthe cylinder 25 which serves to release the brake 14. Two relief valvesare provided for the hydraulic circuit. Relief valve 45 is disposed in aconduit 46 connecting between pressure conduit 31 and the tank returnline 28. Relief valve 47 is disposed in a conduit 48 communicatingbetween conduits 40 and 41. Leakage from the hydraulic motor 10 isconveyed to the tank return line by means of a conduit 50.

Reference is now made to FIGS. 2-7 for a description of the constructionand operation of the four-way control valve 30. This valve is classifiedas being of the spool type in that it has a movable valve member 51 withthe inner operative portion being generally in the form of a spool. Thevalve member 51 is longitudinally reciprocal within the valve body 52and is maintained in fluid-tight relationship by means of O-rings 53 and54 seated in the valve body adjacent the end openings through which thespool member 51 is slidable. One end of the valve member 51 projects asubstantial distance from the valve body 52 end and this end may be usedfor operating the valve by any suitable means. For example, it may beoperated manually either directly, or from a distance by suitablelinkages. Alternatively, the valve member may be actuated electrically,hydraulically or pneumatically, in known manner.

The valve member 51 has an intermediate neutral position in which thehoist is at rest. At one side of neutral the valve member 51 can occupya range of hoist-raising positions while at the opposite side of neutralit can occupy a range of hoist-lowering positions. The construction ofthe valve 30, particularly the construction of the valve or spool member51 thereof, and the way it operates within the valve body 52. will nowbe described. Referring to FIG. 2 it will be seen that the spool member51 has a relatively short neck portion providing a groove 55 and arelatively long neck portion providing a groove 56 which are separatedby a flange section 57 provided with machined tapers 58 and 60 adjacentgroove 56'. At the outer end of the groove 56 on the adjacent fulldiameter portion there is a single taper 61. On the opposite end of thespool portion adjacent the shorter groove 55 the spool is provided withdual tapers 62 and 63 and a narrow cylindrical band 64. It will beunderstood that other tapers may be selected as long as the resultingoperation of the valve is satisfactory. The tapers form annular orificesof variable width in cooperation with the circumferential corners ofadjacent lands as will be described hereinafter.

It will be seen that the groove 56 has a length which exceeds the widthof port 34 plus the lands on opposite sides thereof. Groove 55 isshorter having a length equal to the width of port 36 plus only aportion of the width of one of the adjacent lands.

In FIG. 2 the spool member 51 is in its intermediate and neutralposition in the valve body 52. It will be seen that the pressure inletport 33 communicates through an annular orifice indicated by the pointsor corners ab into the longer groove 56 which is in full communicationwith the port 34 and also with the port 35 through the annular orificebetween points cd. The escape of fluid to tank through the orifice cdprevents pressure from building up in the conduit 40 connected with port34. It will be seen that port 36 is cut off from communication withinlet port 33. The pressure in the inlet 33 under these conditions may,for example, be approximately pounds per square inch (p.s.i.). Since thebrake cylinder 25 is set to open at a substantially higher pressure(e.g. 300 psi.) it will be seen that the hoist will remain at rest asthe brake 14 is set, port 36 is completely shut off, and fluid canfreely escape through orifice c-d to tank through return line 28.

Now assuming that it is desired to operate the hoist system so as toraise a load, the spool member is shifted to the left (downwardly asviewed in FIG. 1) from the position shown in FIG. 2 to the position inFIG. 3. As this movement occurs, it will be seen that an orifice isopened between the points 2 and 1 allowing fluid to flow from thepressure inlet port 33 into the groove 55 and hence into the port 36which communicates with line 41. In the meantime the orifice a--bbecomes restricted due to the taper 58. As this shifting movement of thespool member and orifice variation continues it will be seen that thepressure will build up in the line 41 and decrease in the port 34. Whenthe pressure in line 41 becomes great enough it will operate the motor10 in a hoist raising position. That is, the fluid will enter the motor10 through the conduit 41 and will exit through the conduit 40 so as toreturn to the valve 30 wherein it will pass from the port 34 throughorifice cd into the port 37 and thus discharge to tank by way of returnline 28. It should be noted that during this hoist raising operation thepressure in the port 36 is not controlled by the size orifice ef but bythe size of the orifice ab. In other words, as the latter orificebecomes more restricted a greater portion of the fluid passes throughorifice e- In FIG. 4 the condition is shown in which the spool 51 hasbeen moved all the way to the hoist raising condition. In this conditionit will be seen that point a has moved to a place where there is nolonger an orifice a-b leading from port 33 into the spool groove 56.Accordingly, all of the fluid introduced into the inlet port 33 nowflows through orifice e-f into the groove 55 and port 36. Thus, thecontrol valve 30 is now in the condition where the hoist system exertsmaximum lifting power.

Considering now the operation and conditions of the control valve 30during hoist lowering, the spool member 51 is shifted to the right fromthe neutral position of FIG. 2 (i.e. lowered as viewed in FIG. 1) andpasses through the conditions shown in FIGS. 5-7. In FIG. 5 port 36 iscompletely shut off while orifice a-b is open into the long or widegroove 56 with orifice c-d being appreciably restricted. Because of therestriction of orifice c--d pressure builds up in port 34 to a value(e.g. 300 psi.) which is suflicient to actuate the cylinder and causethe brake 14 to release. Port 36 is on the verge of opening orcommunicating with the tank or discharge port 37. However, as long asthis communication between ports 36 and 37 is not yet established, fluidcannot discharge from the motor 10 and the rotation of this motor istherefore limited to that which is permitted by leakage. This of courseis very slow.

The taper 61 is so designed that as the spool 51 moves further in theload lowering direction to the relative position shown in FIG. 6 aconstant pressure of say 300 p.s.i. is maintained in the port 34.However, a restricted orifice commences to open between points g and hwhich permit-s restricted flow from port 36 into the discharge post 37.Hence, the flow from port 33 of pressure fluid is no longer completelydischarged from orifice cd to tank since now some of it may pass throughline 4%, through the hydraulic motor 10 and out through line 41 back tothe valve 36 through which it is discharged to port 37 through theorifice g-h.

The taper 61 is such that during the balance of hoist lowering theportion of the fluid allowed to flow out through orifice c-d is such toalways maintain a substantially constant pressure of 300 p.s.i., orwhatever value is required to release the brake. However, as the spoolmember 51 is moved further from neutral into the range of hoistlowering, the orifice g-h is increased in width to the point where agreater portion of the hydraulic fluid discharges through port 34 so asto pass through the motor 10 and less discharges to tank through orificecd.

During the various conditions of hoist lowering the function of theorifice c-d is to provide sufficient pressure, e.g. 300 p.s.i., in theline 40 so as to keep the brake released and insure against cavitationin the motor 10. On the other hand, the function of the orifice g-h isto restrict the flow from the motor '10 and hold back the load and thusgive the load proper control.

When the spool member 51 is shifted fully to its extreme right handposition, as shown in FIG. 7, wherein maximum hoist lowering ispermitted the orifice c-d is finally closed so that all of the hydraulicfluid passes out through the port 34, fiows through the hydraulic motor10 to permit lowering, and flows back through the valve and by Way ofthe orifice g-h to tank. Even so, the orifice g-h remains relativelyrestricted so that the flow therethrough is not excessive. In effectmaximum flowthrough is restricted so that it is equal to the overrunning torque of the hydraulic motor 10 under maximum load, plus thepressure required to release the brake. Thus, a given load drives thehydraulic motor 1% as a pump and creates a pressure on the dischargeside of the hydraulic motor. To the pressure of the load must be addedthe pressure on the inlet side of the hydraulic motor it necessary tohold the brake open.

The orifice g-h is designed to limit the maximum flow rate to give thedesired maximum speed of the load and yet insure that the rate 'at whichthe hydraulic motor 10 is turning does not require more fluid than canbe supplied by the pump 5. The latter condition could occur if an extraheavy load were being lowered. This would cause the motor to cavitatedue to its higher speed under these circumstances. However, should thisoccur the pressure in port 34 will promptly drop to atmospheric or lesswith the result that the brake 14 will automatically set since there isno pressure maintained in the lines 40 and 26 to keep it open. Hence theload will be brought under control by the brake setting.

The function of the relief valve is to prevent the hoist from lifting anextra-heavy load. That is, from raising a load which exceeds that forwhich the hydraulic system or 'hydraulic hoist is designed. If anexcessive load should be applied to the hoist, the spool 51 will be putin the full hoist raising position as shown in FIG. 4

in an attempt to raise it. However, if the load is too heavy, excessivepressure starts to build up and the relief valve -45 will open torelieve it. Otherwise, the pump 5 would continue to operate and thesystem would continue to build up pressure until some part failed. Byreason of the pressure relief valve 45 when the pressure reaches thepreset maximum, additional pressure is automatically discharged throughthe valve to the tank return line 28 and the system is thus protected.

The function of the relief valve 47 is to protect the system duringhoist lowering. Thus, if a heavy load is being lowered at maximum speedand the spool member 51 is moved to the neutral position shutting offport 36, flow of fluid from the motor 10 through the line 41 would beautomatically stopped. Damage might well occur under these circumstancesexcept for the fact that the pressure relief valve 47 will open andpermit the sudden surge of pressure to be dissipated or short-circuitedthrough the line 4 8 back through line 40 into the port 34 which is incommunication with the discharge port 35.

It will be seen that control valve 34 provides for excellent controlover a wide range. During hoist-raising the valve 30 can be set so itjust barely lifts the load or it may be set for maximum lifting speed,or for any in termediate speed. Similarly, during hoist lowering, thevalve 3% can be so operated that it just barely moves through controlledslipping of the brake 14, or it can be driven down at maximum speed, orat any intermediate speed. With a given load the operation ispractically constant at any particular setting.

Since certain changes and modifications can be made in the embodimentsof the invention as described and shown in the accompanying drawingswithout departing from the spirit and scope of the invention, it isintended that all matter described above or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. In a hydraulic hoist system adapted to drive a cable drum or the likeand including, (1) a positive displacement pump having a fluid dischargeconnection and a fluid return inlet connection, (2) a reversible rotaryhydraulic motor having two fluid connections, and (3) a brake operablycoupled with said motor, said brake being free-running in the liftdirection of said motor and having pressure means normally applying saidbrake so said motor is not free to turn in the lowering direction, andhaving a hydraulic cylinder unit whereby hydraulic pressure may be usedto overcome said pressure means and release said brake, the improvementwhich comprises: an open-center four-way control valve comprising avalve body having a pressure inlet port, a pair of first and secondports on one side of said inlet port the first being adjacent theretoand the second being non-adjacent, a second pair of third and fourthports on the opposite side of said inlet port, the third port beingadjacent thereto, the fourth port being non-adjacent, and a movablevalve member operable in said valve body having an intermediate neutralposition and a range of hoist-raising positions on one side of neutraland a range of hoistlowering positions on the opposite side of neutral;first conduit means interconnecting said pressure inlet port with thedischarge connection of said positive displacement pump; second conduitmeans interconnecting said first port with the connection of saidhydraulic motor through which fluid exits during hoist raising andthrough which fluid enters during hoist lowering; third conduit meansinterconnecting said third port with the connection of said hydraulicmotor through which fluid enters during hoist raising and through whichfluid exits during hoist lowering; fourth conduit means interconnectingsaid second and fourth ports with said return inlet connection of saidpositive displacement pump; and, fifth conduit means interconnectingsaid hydraulic cylinder unit of said brake with said second conduitmeans; said movable valve member in said neutral position establishing acondition of said valve wherein said pressure inlet port is incommunication with both said first and second ports through a firstorifice and said third port is not in communication with any other port,whereby fluid entering said inlet port can discharge only through saidsecond port; said movable valve member upon being moved from neutralinto said range of hoist-raising positions established a second orificebetween said pressure inlet port and said third port which becomeslarger, while said first orifice providing communication between saidinlet port and said first and second ports becomes smaller and isfinally closed as said valve member moves further into said range ofhoist-shifting positions but with said first and second ports being incontinuous communication with each other during hoist-raising; saidmovable valve member upon being moved from neutral into said range ofhoist-lowering positions first restricting a third orifice into saidsecond port while said third port is not in communication with any otherport thereby increasing the pressure in said first port and said secondand fifth conduit means until said hydraulic cylinder unit is activatedto release said brake, and as said movable valve member moves stillfurther from neutral into said range of hoistlowering positionsestablishing and progressively opening a fourth orifice between saidthird and fourth ports and finally closing said third orifice into saidsecond port whereupon all of the fluid flows out through said firstport, returns through said third port and discharges through said fourthport.

2. The improvement called for in claim 1 wherein: said ports in saidvalve body are provided by spaced circumferential grooves formed in alongitudinal spool-receiving bore, and separated by interior lands; andsaid movable valve member is a spool member having, spaced full diameterportions with an intermediate full diameter flange section therebetween,and necks on opposite sides of said intermediate flange sectionproviding spool grooves for establishing operating communication betweensaid ports, said full diameter portions having tapers formed thereonadjacent the outer ends of said spool grooves, and said flange sectionhaving a taper formed on one end thereof, said tapers providing variableorifices in cooperation with corners of said lands.

3. The improvement called for in claim 1 wherein: said ports in saidvalve body are provided by spaced circumferential grooves of equal widthformed in an elongated spool-receiving bore and separated by interiorlands of equal width; and said movable member is a spool member having,spaced full diameter portions with an intermediate full diameter flangesection therebetween which at all times during operation of saidhydraulic hoist system registers with at least some portion of saidpressure inlet port, and a neck on each side of said intermediate flangesection providing spool grooves for establishing operating communicationbetween said ports, one of said spool grooves being at all times duringoperation in substantially full registration with said first port andhaving a length exceeding the width of said first port and the two landson opposite sides thereof, and the other spool groove being at all timesduring operation in at least partial registration with said third portand having a length equal to the width of said third port plus a portionof the width of one land, said full diameter portions having tapersformed thereon adjacent the outer ends of said spool grooves and saidflange section having a taper on the side toward said longer spoolgroove, said tapers providing variable width annular orifices incooperation with adjacent corners of said lands.

4. In a hydraulic hoist system adapted to drive a cable drum or the likeand including, (1) a positive displacement pump having a fluid dischargeconnection and a fluid return inlet connection, (2) a reversible rotaryhydraulic motor having two fluid connections, and (3) a brake operablycoupled with said motor, said brake being free-running in the liftdirection of said motor and having pressure means normally applying saidbrake so said motor is not free to turn in the lowering direction, andhaving a hydraulic cylinder unit whereby hydraulic pressure may be usedto overcome said pressure means and release said brake, the improvementwhich comprises: control valve means providing first, second, third andfourth variable control orifices each of which during some phases ofoperation of said hoist system from the fastest hoist raising conditionthrough neutral to the slowest hoist lowering condition ranges frombeing fully closed to being fully open, movable orifice regulating meansfor simultaneously regulating said variable orifices, a first pressureinlet port communicating with the inlet sides of said first and secondorifices, a second port communicating between the discharge side of saidfirst orifice and the inlet side of said third orifice, a third portcommunicating between the discharge side of said second orifice and theinlet side of said fourth orifice, first conduit means interconnectingsaid pressure inlet port with the discharge connection of said positivedisplacement pump, second conduit means interconnecting said second portwith the connection of said hydraulic motor through which fluid exitsduring hoist raising and through which fluid enters during hoistlowering, third conduit means interconnecting said third port with theconnection of said hydraulic motor through which fluid enters duringhoist raising and through which fluid exits during hoist lowering,fourth conduit means interconnecting the discharge sides of said thirdand fourth orifices with said return inlet connection of said positivedisplacement pump, and fifth conduit means interconnecting saidhydraulic cylinder unit of said brake with said second conduit means,said control valve means having a neutral condition wherein said firstand third orifices are partly open and said second and fourth orificesare closed whereby all fluid entering said pressure inlet portdischarges through said first and third orifices by way of said secondport while said second and fourth orifices prevent flow through saidmotor, said control valve means having intermediate hoist-raisingconditions wherein said second orifice is partly open, said firstorifice is more restricted than said second orifice and restricts theflow of fluid and regulates the hoist speed, said third orifice is wideropen than in said neutral condition, and said fourth orifice is closed,in said fastest hoist raising condition of said control valve means saidfirst and fourth orifices being closed, and said second and thirdorifices being wide open, said control valve means having a brakerelease condition wherein said first orifice is partly open, said secondand fourth orifices are closed, and said third orifice is restrictedsufficiently to creat enough back pressure in said second and fifthconduit means to release said brake, said control valve means havingintermediate hoist lowering conditions wherein said first orifice iswider open than in said brake release condition, said second orifice isclosed, said third orifice is more restricted than in said brake releasecondition, and said fourth orifice is only slightly open and serves tothrottle the flow and control the hoist speed, and in said slowest hoistlowering condition of said control valve means said first orifice beingwide open, said second and third orifices being closed, and said fourthorifice being wide open but substantially more restricted than saidfirst orifice and serving to throttle the flow of fluid and control thehoist speed.

References Cited in the file of this patent UNITED STATES PATENTS2,407,692 Vickers Sept. 17, 1946 2,416,801 Robinson Mar. 4, 1947

